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Gautam Kumar Deb - One of the best experts on this subject based on the ideXlab platform.
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Evidence of melt/rock interaction in the Cr-spinel bearing wehrlite rocks of Bangriposi, India: Implications for nature of the metasomatic agent
Elsevier, 2018Co-Authors: Tushar Mouli Chakraborti, Arijit Ray, Gautam Kumar DebAbstract:Cr-spinel bearing wehrlite rocks of Bangriposi are found within the multiply deformed metasedimentary rocks of Singhbhum Group belonging to North Singhbhum Mobile Belt of eastern India. Detailed mineralogical and geochemical studies reveal that these rocks have suffered a two-stage alteration involving a deeper level modal and cryptic Metasomatism and a subsequent shallower depth pervasive hydrothermal alteration. Cryptic Metasomatism is defined by elevated LREE contents of the wehrlite and its clinopyroxne grains. Metasomatism induced changes in the modal mineralogy of the rocks include the absence of primary orthopyroxene grains, presence of secondary diopside-phlogopite (now present as vermiculite) defining disequilibrium reaction textures and secondary orthopyroxene rims around serpentinized olivine. The mineralogical and geochemical changes due to the metasomatic event present a contrasting picture in regard to the metasomatic history of the rocks. Possible scenarios involving a single stage or multiple stage Metasomatism events have been discussed while explaining the metasomatic reactions that took place. An attempt has been made to estimate the REE concentrations of the final equilibrating melt from REE contents of clinopyroxene grains of the wehrlite. The possibility of the LREE-enriched equilibrating melt of the wehrlite rocks (the deeper level metasomatic agent) being similar to residual melts from the E-MORB type parental melts of nearby gabbro suite has been ruled out by geochemical modeling. REE abundance patterns of several natural enriched melts have been compared with REE pattern of calculated LREE-enriched equilibrating melt of the wehrlite and most resemblance has been observed with calcic and potassic melts. It is therefore suggested that the Cr-spinel bearing wehrlite rocks of Bangriposi has been affected by a calcio-potassic melt in deeper level, prior to the shallow level serpentinization event. Keywords: Wehrlite, Modal Metasomatism, Cryptic Metasomatism, Vermiculite, Carbonated alkaline mel
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Evidence of melt/rock interaction in the Cr-spinel bearing wehrlite rocks of Bangriposi, India: Implications for nature of the metasomatic agent
Geoscience Frontiers, 2018Co-Authors: Tushar Mouli Chakraborti, Arijit Ray, Gautam Kumar DebAbstract:Abstract Cr-spinel bearing wehrlite rocks of Bangriposi are found within the multiply deformed metasedimentary rocks of Singhbhum Group belonging to North Singhbhum Mobile Belt of eastern India. Detailed mineralogical and geochemical studies reveal that these rocks have suffered a two-stage alteration involving a deeper level modal and cryptic Metasomatism and a subsequent shallower depth pervasive hydrothermal alteration. Cryptic Metasomatism is defined by elevated LREE contents of the wehrlite and its clinopyroxne grains. Metasomatism induced changes in the modal mineralogy of the rocks include the absence of primary orthopyroxene grains, presence of secondary diopside-phlogopite (now present as vermiculite) defining disequilibrium reaction textures and secondary orthopyroxene rims around serpentinized olivine. The mineralogical and geochemical changes due to the metasomatic event present a contrasting picture in regard to the metasomatic history of the rocks. Possible scenarios involving a single stage or multiple stage Metasomatism events have been discussed while explaining the metasomatic reactions that took place. An attempt has been made to estimate the REE concentrations of the final equilibrating melt from REE contents of clinopyroxene grains of the wehrlite. The possibility of the LREE-enriched equilibrating melt of the wehrlite rocks (the deeper level metasomatic agent) being similar to residual melts from the E-MORB type parental melts of nearby gabbro suite has been ruled out by geochemical modeling. REE abundance patterns of several natural enriched melts have been compared with REE pattern of calculated LREE-enriched equilibrating melt of the wehrlite and most resemblance has been observed with calcic and potassic melts. It is therefore suggested that the Cr-spinel bearing wehrlite rocks of Bangriposi has been affected by a calcio-potassic melt in deeper level, prior to the shallow level serpentinization event.
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evidence of melt rock interaction in the cr spinel bearing wehrlite rocks of bangriposi india implications for nature of the metasomatic agent
Geoscience frontiers, 2017Co-Authors: Tushar Mouli Chakraborti, Arijit Ray, Gautam Kumar DebAbstract:Abstract Cr-spinel bearing wehrlite rocks of Bangriposi are found within the multiply deformed metasedimentary rocks of Singhbhum Group belonging to North Singhbhum Mobile Belt of eastern India. Detailed mineralogical and geochemical studies reveal that these rocks have suffered a two-stage alteration involving a deeper level modal and cryptic Metasomatism and a subsequent shallower depth pervasive hydrothermal alteration. Cryptic Metasomatism is defined by elevated LREE contents of the wehrlite and its clinopyroxne grains. Metasomatism induced changes in the modal mineralogy of the rocks include the absence of primary orthopyroxene grains, presence of secondary diopside-phlogopite (now present as vermiculite) defining disequilibrium reaction textures and secondary orthopyroxene rims around serpentinized olivine. The mineralogical and geochemical changes due to the metasomatic event present a contrasting picture in regard to the metasomatic history of the rocks. Possible scenarios involving a single stage or multiple stage Metasomatism events have been discussed while explaining the metasomatic reactions that took place. An attempt has been made to estimate the REE concentrations of the final equilibrating melt from REE contents of clinopyroxene grains of the wehrlite. The possibility of the LREE-enriched equilibrating melt of the wehrlite rocks (the deeper level metasomatic agent) being similar to residual melts from the E-MORB type parental melts of nearby gabbro suite has been ruled out by geochemical modeling. REE abundance patterns of several natural enriched melts have been compared with REE pattern of calculated LREE-enriched equilibrating melt of the wehrlite and most resemblance has been observed with calcic and potassic melts. It is therefore suggested that the Cr-spinel bearing wehrlite rocks of Bangriposi has been affected by a calcio-potassic melt in deeper level, prior to the shallow level serpentinization event.
Tushar Mouli Chakraborti - One of the best experts on this subject based on the ideXlab platform.
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Evidence of melt/rock interaction in the Cr-spinel bearing wehrlite rocks of Bangriposi, India: Implications for nature of the metasomatic agent
Elsevier, 2018Co-Authors: Tushar Mouli Chakraborti, Arijit Ray, Gautam Kumar DebAbstract:Cr-spinel bearing wehrlite rocks of Bangriposi are found within the multiply deformed metasedimentary rocks of Singhbhum Group belonging to North Singhbhum Mobile Belt of eastern India. Detailed mineralogical and geochemical studies reveal that these rocks have suffered a two-stage alteration involving a deeper level modal and cryptic Metasomatism and a subsequent shallower depth pervasive hydrothermal alteration. Cryptic Metasomatism is defined by elevated LREE contents of the wehrlite and its clinopyroxne grains. Metasomatism induced changes in the modal mineralogy of the rocks include the absence of primary orthopyroxene grains, presence of secondary diopside-phlogopite (now present as vermiculite) defining disequilibrium reaction textures and secondary orthopyroxene rims around serpentinized olivine. The mineralogical and geochemical changes due to the metasomatic event present a contrasting picture in regard to the metasomatic history of the rocks. Possible scenarios involving a single stage or multiple stage Metasomatism events have been discussed while explaining the metasomatic reactions that took place. An attempt has been made to estimate the REE concentrations of the final equilibrating melt from REE contents of clinopyroxene grains of the wehrlite. The possibility of the LREE-enriched equilibrating melt of the wehrlite rocks (the deeper level metasomatic agent) being similar to residual melts from the E-MORB type parental melts of nearby gabbro suite has been ruled out by geochemical modeling. REE abundance patterns of several natural enriched melts have been compared with REE pattern of calculated LREE-enriched equilibrating melt of the wehrlite and most resemblance has been observed with calcic and potassic melts. It is therefore suggested that the Cr-spinel bearing wehrlite rocks of Bangriposi has been affected by a calcio-potassic melt in deeper level, prior to the shallow level serpentinization event. Keywords: Wehrlite, Modal Metasomatism, Cryptic Metasomatism, Vermiculite, Carbonated alkaline mel
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Evidence of melt/rock interaction in the Cr-spinel bearing wehrlite rocks of Bangriposi, India: Implications for nature of the metasomatic agent
Geoscience Frontiers, 2018Co-Authors: Tushar Mouli Chakraborti, Arijit Ray, Gautam Kumar DebAbstract:Abstract Cr-spinel bearing wehrlite rocks of Bangriposi are found within the multiply deformed metasedimentary rocks of Singhbhum Group belonging to North Singhbhum Mobile Belt of eastern India. Detailed mineralogical and geochemical studies reveal that these rocks have suffered a two-stage alteration involving a deeper level modal and cryptic Metasomatism and a subsequent shallower depth pervasive hydrothermal alteration. Cryptic Metasomatism is defined by elevated LREE contents of the wehrlite and its clinopyroxne grains. Metasomatism induced changes in the modal mineralogy of the rocks include the absence of primary orthopyroxene grains, presence of secondary diopside-phlogopite (now present as vermiculite) defining disequilibrium reaction textures and secondary orthopyroxene rims around serpentinized olivine. The mineralogical and geochemical changes due to the metasomatic event present a contrasting picture in regard to the metasomatic history of the rocks. Possible scenarios involving a single stage or multiple stage Metasomatism events have been discussed while explaining the metasomatic reactions that took place. An attempt has been made to estimate the REE concentrations of the final equilibrating melt from REE contents of clinopyroxene grains of the wehrlite. The possibility of the LREE-enriched equilibrating melt of the wehrlite rocks (the deeper level metasomatic agent) being similar to residual melts from the E-MORB type parental melts of nearby gabbro suite has been ruled out by geochemical modeling. REE abundance patterns of several natural enriched melts have been compared with REE pattern of calculated LREE-enriched equilibrating melt of the wehrlite and most resemblance has been observed with calcic and potassic melts. It is therefore suggested that the Cr-spinel bearing wehrlite rocks of Bangriposi has been affected by a calcio-potassic melt in deeper level, prior to the shallow level serpentinization event.
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evidence of melt rock interaction in the cr spinel bearing wehrlite rocks of bangriposi india implications for nature of the metasomatic agent
Geoscience frontiers, 2017Co-Authors: Tushar Mouli Chakraborti, Arijit Ray, Gautam Kumar DebAbstract:Abstract Cr-spinel bearing wehrlite rocks of Bangriposi are found within the multiply deformed metasedimentary rocks of Singhbhum Group belonging to North Singhbhum Mobile Belt of eastern India. Detailed mineralogical and geochemical studies reveal that these rocks have suffered a two-stage alteration involving a deeper level modal and cryptic Metasomatism and a subsequent shallower depth pervasive hydrothermal alteration. Cryptic Metasomatism is defined by elevated LREE contents of the wehrlite and its clinopyroxne grains. Metasomatism induced changes in the modal mineralogy of the rocks include the absence of primary orthopyroxene grains, presence of secondary diopside-phlogopite (now present as vermiculite) defining disequilibrium reaction textures and secondary orthopyroxene rims around serpentinized olivine. The mineralogical and geochemical changes due to the metasomatic event present a contrasting picture in regard to the metasomatic history of the rocks. Possible scenarios involving a single stage or multiple stage Metasomatism events have been discussed while explaining the metasomatic reactions that took place. An attempt has been made to estimate the REE concentrations of the final equilibrating melt from REE contents of clinopyroxene grains of the wehrlite. The possibility of the LREE-enriched equilibrating melt of the wehrlite rocks (the deeper level metasomatic agent) being similar to residual melts from the E-MORB type parental melts of nearby gabbro suite has been ruled out by geochemical modeling. REE abundance patterns of several natural enriched melts have been compared with REE pattern of calculated LREE-enriched equilibrating melt of the wehrlite and most resemblance has been observed with calcic and potassic melts. It is therefore suggested that the Cr-spinel bearing wehrlite rocks of Bangriposi has been affected by a calcio-potassic melt in deeper level, prior to the shallow level serpentinization event.
Chang-hao Shi - One of the best experts on this subject based on the ideXlab platform.
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Geology and fluid geochemistry of the Na-Metasomatism U deposits in the Longshoushan uranium metallogenic belt, NW China: Constraints on the ore-forming process
Ore Geology Reviews, 2020Co-Authors: Jun Zhong, Sheng-yun Wang, Gu Dazhao, Cai Yuqi, Hong-hai Fan, Chang-hao ShiAbstract:Abstract The Longshoushan belt in Gansu Province is a very important uranium metallogenic belt in Northwest China and contains a series of different types (magmatic, Na-Metasomatism, supergenetic) of uranium deposits and occurrences. Of all these mineralization types, the Na-Metasomatism type is the most predominant with great potential, represented by two Na-Metasomatism uranium deposits (Xinshuijing and Jiling). Different from the fluorite-, illite-, quartz-dominated alteration minerals in other hydrothermal uranium mineralization system, the Na-Metasomatism type uranium deposits are characterized by the unique albite-dominated (up to 90 vol%) alteration mineral assemblage, which is referred to albitite in many literatures. All the uranium orebodies in both the Xinshuijing and Jiling deposits are hosted within the metasomatic albitites, and controlled by the subsidiary faults of the regional Malugou Fault. The mineralization process in both deposits can be divided into four stages, namely: the Na-Metasomatism stage, U mineralization stage, post-mineralization stage and supergene mineralization stage. The Na-Metasomatism stage is predominantly composed of albite (with hematite staining), with minor chlorite and anatase, while the U mineralization stage is characterized by the occurrence of uranium minerals (mostly pitchblende), intergrown with some tiny albite, calcite, chlorite, pyrite, apatite, REE-minerals and sometimes hydrothermal zircons. The mineral assemblages of the Na-Metasomatism stage and U mineralization stage are too intimately related to each other and might be the products of the evolution from the same ore-forming fluids. The post-mineralization stage is mainly the calcite-quartz veinlets or occur as aggregate clusters, while the supergene mineralization stage includes mineral assemblage of secondary uranium mineralization-clay minerals (e.g. kaolinite)-limonite. Mineralogical studies and comparison of major and trace elements assay results between fresh biotite granite (predominate host rocks), albitite and uranium ores suggest that the ore-forming fluids resulting in the formation of the Na-Metasomatism alteration are oxidized and rich in Na, Sc, V, Cr, Co, Ni, U, Th, while the ore-forming fluids of the U mineralization stage are relatively reduced and rich in heavy rare earth elements, U, Th, PO34-. Fluid inclusion and calcite C-O isotope studies indicate that the ore-forming fluids are meteoric water-dominated, which circulated at depth (~8 km, by fluid inclusion geobarometer) and scavenged uranium from the host biotite granites and metamorphic rocks of the Longshoushan Group. The ore precipitation is mainly attributed to physicochemical changes (fO2, temperature, fluid composition) from fluid-rock interaction and further temperature decrease of the ore-forming fluids, while fluid boiling and fluid mixing processes are limited. The proposed ore-forming process is not only important for the understanding of the ore genesis for the Na-Metasomatism mineralization systems in Longshoushan, but also highlights the significance of albite alteration, which could be used as an important indicator during further uranium exploration.
W Wang - One of the best experts on this subject based on the ideXlab platform.
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Metasomatism of garnet peridotite from jiangzhuang southern sulu uhp belt constraints on the interactions between crust and mantle rocks during subduction of continental lithosphere
Journal of Metamorphic Geology, 2011Co-Authors: Z M Zhang, X Dong, J G Liou, W WangAbstract:The Jiangzhuang ultrahigh-pressure (UHP) metamorphic peridotite from south Sulu, eastern China occurs as a layer within gneiss with eclogite blocks, and consists of coarse-grained garnet porphyroblasts and a fine-grained matrix assemblage of garnet + forsterite + enstatite + diopside ± phlogopite ± Ti-clinohumite ± magnesite. Both types of garnet are characterized by high MgO content and depletion of light rare earth element (LREE) and enrichment of heavy rare earth element, but the matrix garnet has lower MgO, TiO2 and higher Cr2O3 and REE contents. Diopside displays LREE enrichment, and has low but variable large-ion lithophile element (LILE) contents. Phlogopite is a major carrier of LILE. Ti-clinohumite contains high Nb, Ta, Cr, Ni, V and Co contents. The P–T conditions of 4.5–6.0 GPa and 850–950 °C were estimated for matrix mineral assemblages. Most peridotites are depleted in Al2O3, CaO and TiO2, and enriched in SiO2, K2O, REE and LILE. In contrast to phlogopite-free peridotites, the phlogopite-bearing peridotites have higher K2O, Zr, REE and LILE contents. Zircon occurs only in the phlogopite-bearing peridotites, shows no zoning, with low REE contents and Th/U ratios, and yields tight U–Pb ages of 225–220 Ma, indicating the peridotites experienced consistent Triassic UHP metamorphism with subducted supercrustal rocks. These data demonstrate that the Jiangzhuang peridotites were derived from the depleted mantle wedge of the North China Craton, and experienced various degrees of Metasomatism. The phlogopite-free peridotites may have been subjected to an early cryptic Metasomatism at UHP conditions of the mantle wedge, whereas the phlogopite-bearing peridotites were subjected to a subsequent strong Metasomatism, characterized by distinctly enrichment in LILE, LREE, Zr and K as well as the growth of zircon and volatile-bearing minerals at UHP subduction conditions. The related Metasomatism may have resulted from the filtration of fluids sourced mainly from deeply subducted supracrustal rocks.
Vadim S. Kamenetsky - One of the best experts on this subject based on the ideXlab platform.
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mantle melting versus mantle Metasomatism the chicken or the egg dilemma
Chemical Geology, 2017Co-Authors: Ekaterina S. Kiseeva, Vadim S. Kamenetsky, Gregory M. Yaxley, Simon R. SheeAbstract:Most eclogitic mantle xenoliths brought to the surface exhibit a certain degree of enrichment with incompatible elements, usually attributed to the effect of mantle Metasomatism by a putative metasomatic fluid. The metasomatic overprint is represented mainly by enrichments in Na, K, Ba, Ti and LREE and the original source of this fluid remains unknown. In this paper, we present a detailed petrological study of a typical eclogitic mantle xenolith from the Roberts Victor kimberlite mine in South Africa. We find that its textural and mineralogical features present strong evidence for incipient melting. The melting assemblage we observe did not necessarily require introduction of additional components, that is: in-situ melting alone could produce highly incompatible element enriched melt without involvement of a hypothetical and speculative “metasomatic event”. Due to the higher abundance in incompatible elements and lower solidus temperature than peridotites, mantle eclogites, some of which represent previously subducted oceanic crust, are much more plausible sources of mantle Metasomatism, but on the other hand, they can be considered as highly metasomatised themselves. This brings us to the “chicken or egg” dilemma – was the secondary mineral assemblage in mantle lithologies a result or a source of mantle Metasomatism?
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Mantle melting versus mantle Metasomatism – “The chicken or the egg” dilemma
Chemical Geology, 2017Co-Authors: Ekaterina S. Kiseeva, Vadim S. Kamenetsky, Gregory M. Yaxley, Simon R. SheeAbstract:Most eclogitic mantle xenoliths brought to the surface exhibit a certain degree of enrichment with incompatible elements, usually attributed to the effect of mantle Metasomatism by a putative metasomatic fluid. The metasomatic overprint is represented mainly by enrichments in Na, K, Ba, Ti and LREE and the original source of this fluid remains unknown. In this paper, we present a detailed petrological study of a typical eclogitic mantle xenolith from the Roberts Victor kimberlite mine in South Africa. We find that its textural and mineralogical features present strong evidence for incipient melting. The melting assemblage we observe did not necessarily require introduction of additional components, that is: in-situ melting alone could produce highly incompatible element enriched melt without involvement of a hypothetical and speculative “metasomatic event”. Due to the higher abundance in incompatible elements and lower solidus temperature than peridotites, mantle eclogites, some of which represent previously subducted oceanic crust, are much more plausible sources of mantle Metasomatism, but on the other hand, they can be considered as highly metasomatised themselves. This brings us to the “chicken or egg” dilemma – was the secondary mineral assemblage in mantle lithologies a result or a source of mantle Metasomatism?
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Nickel-rich Metasomatism of the lithospheric mantle by pre-kimberlitic alkali-S-Cl-rich C-O-H fluids
Contributions to Mineralogy and Petrology, 2012Co-Authors: Andrea Giuliani, Vadim S. Kamenetsky, Mark A. Kendrick, David Phillips, Karsten GoemannAbstract:Metasomatism of the lithospheric mantle sometimes produces unusual assemblages containing native metals and alloys, which provide important insight into metasomatic processes in the mantle. In this study, we describe the metasomatic enrichment of a refractory harzburgite xenolith in Ni, Fe and, to a lesser extent, Cu, Co, As and Sb. The xenolith (XM1/422) derives from the Bultfontein kimberlite (Kimberley, South Africa) and hosts Ni mineralisation that includes native nickel (Ni84.5-98.0), heazlewoodite (Ni3S2) and Ni-rich silicates (e.g. up to 37.5 wt % NiO in olivine, and 22.4 wt % NiO in phlogopite). The presence of several mineral phases enriched in alkali and volatile species (e.g. phlogopite, phosphates, carbonates, chlorides, djerfisherite) indicates that the transition metal cations were likely introduced during Metasomatism by alkali-rich C–O–H fluids or alkali-carbonate melts. It is postulated that sulphide breakdown and fluid reaction with refractory mantle rocks contributed to the fluid’s enrichment in Ni and other metallic cations. The Ni-rich assemblages of xenolith XM1/422 show local chemical disequilibrium, and modelling of the Ni diffusion profiles adjacent to olivine-native nickel and olivine-heazlewoodite grain boundaries, suggests a close temporal relationship between Ni-rich Metasomatism and subsequent entrainment by the kimberlite magma. However, metal-rich Metasomatism has also been observed in other lithospheric mantle domains, including orogenic peridotitic massifs and the suboceanic mantle; regions unaffected by kimberlite magmatsim. As micro-scale occurrences of metallic phases are easily overlooked, it is possible that metal-rich Metasomatism is more widespread in the Earth’s mantle than previously recognised.
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Carbonatite Metasomatism in the southeastern Australian lithosphere
Journal of Petrology, 1998Co-Authors: Gregory M. Yaxley, David H. Green, Vadim S. KamenetskyAbstract:New mineralogical and geochemical data from a suite of glass +/- apatite +/- amphibole +/- phlogopite +/- carbonate-bearing spinel wehrlite, lherzolite and harzburgite xenoliths from the Newer Volcanics, southeastern Australia, are consistent with metasomatic interactions between harzburgitic or refractory lherzolitic lithosphere, and penetrative sodic dolomitic carbonatite melts. Metasomatism occurred when ascending dolomitic carbonatites crossed the reaction enstatite + dolomite = forsterite + diopside + CO2 at similar to 1.5-2.0 GPa, resulting in partial to complete replacement of primary orthopyroxene by sodic clinopyroxene, together with crystallization of apatite, amphibole and phlogopite, and release of CO2-rich fluid. In the sample suite examined, the minimum amount of carbonatite melt may be estimated on the assumption that Metasomatism occurred in a closed system, and that the precursor lithology was clinopyroxene-poor harzburgite. The derivative wehrlite compositions require 6-12% carbonatite addition, the lherzolites require similar to 8% or less, and the harzburgites require minimal addition of carbonatite. However, Metasomatism probably also involved an open system component, during which by partitioning relationships with the reacting carbonatite, resulting in loss from the metasomatized volume of a fugitive, siliceous, aluminous, alkali- and LILE-enriched silicate melt.